Variable-capacity vane pumps

ABSTRACT

Variable-capacity pump wherein the movable radial vanes engage the inner surface of a ring receiving the pressure exerted by a sealing member coacting with the pump casing and with the cover to form a chamber communicating through an orifice with the highpressure side of the pump, the active surface of this chamber corresponding to a valve whereat the force resulting from the pressure exerted on said surface is substantially equal to but higher than the sum of the efforts due to the fluid which tend to separate said sealing member from said ring.

Waited States Patent Maistrelli 1 Feb. 15, 1972 [54] VARIABLE-CAPACITY VANE PUMPS [72] Inventor: Roger Maistrelli, Billancourt, France [22] Filed: Mar. 30, 1970 [21] Appl.No.: 23,780

[30] Foreign Application Priority Data Apr. 9, 1969 France ..6910967 [52] U.S.Cl ..418/30,4l8/133,418/135 [51] Int. Cl ..F0lc 21/16, FOlc 19/08, F04c 27/00 [58] FieldofSearch ..4l8/30,131, 133,135,132, 418/24-27; 417/220 [56] References Cited UNITED STATES PATENTS 2,708,884 5/1955 Deschamps ..4l8/135 2,949,081 8/ l 960 Deschamps ..418/30 2,490,115 12/1949 Clarke 418/135 2,685,256 8/1954 Humphreys 148/133 2,782,724 2/1957 Humphreys. 418/133 3,209,699 10/1965 Baghuis ..4l8/25 Primary ExaminerWilliam L. Freeh Assistant Examiner-John J. Vrablik Attorney-Stevens, Davis, Miller & Mosher ABSTRACT 1 Claims, 2 Drawing Figures slim all VARIABLE-CAPACITY VANE PUMPS The present invention relates in general to vane pumps and has particular reference to a variable-capacity vane pump designed for pumping compressible fluids, especially a pump intended for operating under lowor medium-pressure conditions, i.e., from a few bars to about lOO bars (about 50 to 1,500 p.s.i.) for supplying hydropneumatic circuits of machine tools, public works vehicles and other apparatus and machinery requiring as a rule pumps capable of delivering a given output or amount of fluid under a predetermined pressure.

To obtain a given fluid output a pump may be driven at a constant speed by means of an electric motor. Now this solution, although practicable and normally used in stationary industrial installations, is obviously ill adapted for installations and machinery using a heat engine. In this case, if it is desired to maintain a constant fluid output irrespective of the heat engine speed, two types of pumps may be used:

l. a variable-capacity pump capable of delivering a sufficient fluid output even when the heat engine operates at minimum speed. When the heat engine speed is in creased, the cylinder or like capacity of the pump is reduced proportionally in order to keep the fluid output at a substantially constant value;

2. a constant-capacity pump designed for delivering the desired fluid output when the heat engine operates at minimum speed. When the engine speed is accelerated, an increasing fraction of the pump output is diverted and returned to the reservoir (or to the suction port of the pump) in order to keep the useful fluid output at a constant value. The member generally employed for keeping the useful pump output at a steady value by diverting the excess output to the reservoir is referred to as the constant output valve."

However, in these known arrangements care must be taken that the fluid pressure does not exceed a predetermined value in order to protect the pump and the other circuit components against overloads.

It is also known that various solutions are available for delivering a pressure under a predetermined pressure, namely:

the use of a variable-capacity pump of which the fluid output is adjusted automatically to the desired value irrespective of the speed ofthe driving heat engine or electric motor;

the use of a constant-capacity pump delivering an output sufficient to meet any output demand irrespective of the speed of the pump-driving motor or engine. In this case the pressure is maintained at the requisite value by allowing the excess fluid output to flow back to the reservoir through a so-called discharge or check" valve so as to keep the pressure at a constant value.

The use of variable-capacity pumps is desirable in that they afford a substantial improvement in the circuit efficiency. In fact, with these pumps the output is constantly kept at the value just necessary for ensuring a normal circuit operation. In hitherto known arrangements of this character, i.e., utilizing constant-capacity pumps, the higher the speed of the pumpdriving motor or engine, the greater the output fraction returned to the reservoir. Under these conditions, it is clear that the chiefinconvenience of these known solutions is a considerable amount of wasted energy, attended by the following consequences:

on the one hand, a substantial loss of efficiency, which may reduce the available power of the pump-driving motor or engine if the latter is intended for other applications, such as the operation of the hydraulic pump of a power-assisted or servoaction steering mechanism;

on the other hand, the transformation of the lost energy into heat most likely to increase the circuit temperature. Under these conditions designer may be led to either increase the volume occupied by the fluid in the circuit, or resort to a heat exchanger.

Considering the foregoing, the use of variable-capacity pumps should have become extremely popular, but the reason having heretofore prevented the universal use of these pumps is the extremely high degree of precision required in the machining of their component elements and also the leakage which exceeds that of other pump types having a fixed capacity. As a consequence, their pressure is generally restricted to moderate values, to prevent the gain in energy, resulting from the use of a variable-capacity pump, from being compensated by higher internal leakage values.

It is the essential object of the present invention to provide an improved variable-capacity vane pump adapted to avoid the various inconveniences set forth hereinabove. This pump, comprising a hollow casing formed with a cylindrical peripheral inner surface and a coaxial rotor rigid with a driving shaft and provided with radially disposed and angularly spaced movable vanes forming pump chambers by riding on the inner cylindrical surface of a ring member adapted to pivot in a transverse plane about a fixedaxis, said ring member having a front face bearing against the pump casing and its other front face pressed by a sealing member crowned by a cover and formed with two external cylindrical surfaces having a circular base which are shiftable both axially and radially, is characterized essentially in that said sealing member coacts with the pump casing and the cover to constitute a fluid chamber communicating via an orifice with the high-pressure side of the pump, the active surface of this chamber corresponding to a value whereat the force resulting from the pressure exerted on said surface is substantially equal to but higher than the sum of the efforts due to the fluid tending to separate said sealing member from said ring member.

Other features characterizing this invention will appear as the following description proceeds with reference to the attached drawing illustrating diagrammatically a typical form of embodiment of the pump of this invention which is given by way ofexample. In the drawing:

FIG. 1 is a longitudinal axial section ofthe pump, and

FIG. 2 is a cross section taken along the line llll of FIG. I.

The pump illustrated in the drawing comprises a casing 1 in which a substantially cylindrical rotor 2 is rotatably mounted about an axis 0, which is the central axis of the casing l. A key 4 locks the rotor 2 to the driving shaft 3 journaled in bearings 5. The rotor 2 comprises a series of radial, angularly spaced notches 6 in which the movable members usually referred to as vanes" but consisting in this example of cylindrical rollers are slidably mounted. However, any other suitable vanes types may be used, such as parallelipipedic, prismatic or other vanes. The vanes 7 form in conjunction with the inner surface 8 of a ring 9 as many chambers 10. This ring 9 is set offcenter to the rotor axis 0 as shown by the distance e (FIG. 2), and acts as a cam member. A sliding control member 11 formed with a notch 12 engaged by a stud 13 carried by the outer periphery of ring 9 is movable in the bore ofa tangent cylinder 14 and constitutes, with its face 15 and the bottom 16 of the cylinder, a chamber 17 adapted to receive hydraulic control fluid through an inlet union 18. A spring 19 reacts on the one hand against the opposite face 20 of sliding member 11, and on the other hand against a plug 21 formed with an inner groove receiving a gasket or seal 22. The plug 21 is held against movement by a circlip 23.

The pump casing 1 comprises an inlet port 24 and an outlet port 25 of arcuate configuration as currently known in the art. The ring 9 engages with one face 26 a shouldered portion of casing 1.

A flange 27 constituting the extension of the fluid inlet and outlet ports 24, 25 fits with a cylindrical outer surface 28 in a bore 29 formed in the pump casing l and engages with its inner front face 30 the ring 9. One or a plurality of springs 3] keep the flange 27 in contact with the ring 9. A cover or cap 32 fitting in a cylindrical eccentric surface 33 of flange 27 and secured to the casing l by means of screws 34 holds the spring or springs 31. This cover 32 comprising a fluid inlet 24' forms with the flange 27 a chamber 35 connected through a passage 36 with the pump outlet port 25. This chamber 35 has a wall 37 receiving the output pressure of the pump. A pair of 0- rings 38 and 39 in flange 27 and another O-ring 40 in the pump casing l in the joint plane ofcover 32 seal the assembly.

This pump operates as follows:

The ring 9 having its lower portion pivoted in the casing l by means of a roller 41 fitting in a corresponding recess of said casing is adjustable in relation to the rotor axis by pivoting about the axis 0' of roller 41 from an initial position in which the axis of ring 9 is coincident with the axis 0 of the pump casing, up to a maximum eccentric value 2 corresponding to the maximum volumetric capacity of the pump. This adjustment is controlled by removing hydraulic fluid from the chamber 17 at the rear end of sliding member 11.

lt is known that the volume of each chamber of the pump varies as the rotor 2 operates, in order to produce the necessary pumping action. Obviously, the magnitude of the eccentricity e of ring 9 in relation to rotor 2 controls the change of volume in said chambers 10 and therefore the pump capacity. The flange 27 can rotate moderately about axes perpendicular to the pump axis and engages the ring 9 in order to push the face 26 thereof against the shoulder machined in the casing l. The forces urging the flange 27 against the ring 9 are produced on the one hand by the moderate pressure of springs 31 and on the other hand by the pump output pressure exerted in chamber 35.

The dimensions of chamber 35 (and therefore the diameters of cylinders 28 and 33) are so calculated that the force pressing the flange 27 against ring 9 is only slightly greater than that created by the fluid pressure within the ring and tending to push the flange 27. On the other hand, the center of gravity of surface 37 (or the point of application of the pressure efforts) is substantially coincident with the point of application of the forces of the inner pressures to ring 9. I

These conditions are therefore such as to cause a movement of ring 9 and therefore a change in the volumetric capacity of the pump by using moderate efforts and with negligible leakage.

The pump according to this invention is attended by the following advantageous features:

Since the flange 27 is kept in steady contact with ring 9, leakages are either extremely reduced or null. Now as the steady contact between flange 27 and ring 9 is due to the fluid pressure prevailing in chamber 35, it is no more necessary to machine in the casing a cavity for the ring which has a very accurate depth; on the other hand, and consequently, any problem concerning a straight parallel relationship between the bottom of this cavity and the ring and cover is definitely eliminated.

Besides, as the flange 27 in its inoperative position is kept in engagement with the ring 9 by one or more low-force springs 31, it is clear that when starting in the cold state a high-viscosity fluid can cause the flange 27 to be slightly lifted, thus avoiding any risk of seizing parts as a consequence of thermal discrepancies. When the viscosity of the fluid has dropped to the proper level the springs 31 will press the flange 27 against the ring 9, thus permitting the rated pumping action.

The above-described pump type is particularly advantageous inter alia for the following applications:

Linn

1. ln power-assisted steering mechanism of highand medium-duty trucks and tractors, buses and private cars. In fact, these circuits require as a rule a very small amount of hydraulic fluid (the reservoir capacity usually ranges from 0.1 to 0.4 gallon). Therefore, it is a frequent occurrence that in case of abnormal driving conditions, such as uphill mountain driving at high engine speed and low vehicle speed, the oil in the circuit becomes overheatedand causes a rapid wear and tear of the components, and therefore serious damages and seizing thereof. This drawback is overcome by using the variable-output pump.

2. As an over-feed pump for converters of the type used in automatic transmissions and hydrostatic transmission circuits. In this case high outputs are sometimes required and a useless waste of power must be prevented to preserve a reasonable total efficiency of the transmission while avoiding heat losses.

in general, this pump type is applicable to advantage to all circuits operating under lowand medium-pressure conditions.

While the invention has been described with reference to certain illustrative embodiments, it is not intended that it be limited thereby except in so far as appears in the accompanying claims.

What is claimed as new is: v

l. A variable-capacity vane pump comprising a hollow casing formed with a cylindrical inner peripheral surface and having a low pressure fluid inlet and a high-pressure fluid outlet, a coaxial rotor in the casing rigid with a driving shaft, sliding radial vanes disposed in notches provided in the rotor at spaced intervals, a ring member inside said inner peripheral surface adapted to pivot in a transverse plane about a fixed axis and forming pumping chambers in conjunction with said sliding radial vanes, said motor and said casing, a sealing member crowned by a cover, said ring member having a first front face engaging the pump casing and a second front face opposite to the first and pressed by an effort exerted by said sealing member having two external cylindrical surfaces each with a circular base which are staggered both axially and radially on this sealing member, said sealing member being kept in contact with said ring member by at least one resilient member and coacting with'the pump casing and with said cover to constitute a fluid chamber which communicates with the high-pressure side of the pump, wherein the active surfaCe of said fluid chamber is defined by a cylindrical surface of said sealing member fitting in said pump casing and by an eccentric cylindrical surfaCe of said sealing member receiving said cover, said chamber surface corresponding to a value for which the pressure force exerted on said surfaCe is substantially equal to but greater than the sum of the forces due to the fluid pressure tending to separate said sealing member from said ring member, the point of application of this pressure force exerted on said surface of the fluid chamber being sub stantially coincident with the point of application of the resultant of the forces tending to separate said sealing member from said ring member. 

1. A variable-capacity vane pump comprising a hollow casing formed with a cylindrical inner peripheral surface and having a low pressure fluid inlet and a high-pressure fluid outlet, a coaxial rotor in the casing rigid with a driving shaft, sliding radial vanes disposed in notches provided in the rotor at spaced intervals, a ring member inside said inner peripheral surface adapted to pivot in a transverse plane about a fixed axis and forming pumping chambers in conjunction with said sliding radial vanes, said motor and said casing, a sealing member crowned by a cover, said ring member having a first front face engaging the pump casing and a second front face opposite to the first and pressed by an effort exerted by said sealing member having two external cylindrical surfaces each with a circular base which are staggered both axially and radially on this sealing member, said sealing member being kept in contact with said ring member by at least one resilient member and coacting with the pump casing and with said cover to constitute a fluid chamber which communicates with the high-pressure side of the pump, wherein the active surfaCe of said fluid chamber is defined by a cylindrical surface of said sealing member fitting in said pump casing and by an eccentric cylindrical surfaCe of said sealing member receiving said cover, said chamber surface corresponding to a value for which the pressure force exerted on said surfaCe is substantially equal to but greater than the sum of the forces due to the fluid pressure tending to separate said sealing member from said ring member, the point of application of this pressure force exerted on said surface of the fluid chamber being substantially coincident with the point of application of the resultaNt of the forces tending to separate said sealing member from said ring member. 